1. Field of the Invention
This invention relates to a method of treating influenza and, more specifically, it relates to introducing intranasally into a patient a prophylactically or therapeutically effective dosage of an attenuated live influenza virus to effect immediate interference with the growth of said influenza virus.
2. Description of the Prior Art
Influenza is currently the sixth leading cause of death in the United States. Particularly vulnerable are the very old and very young which have a higher than average influenza mortality rate.
As influenza epidemics and pandemics can be extremely devastating, particularly in high risk populations, such as retirement communities for senior citizens and daycare centers caring for infants, prompt action to attack the virus is critical. Unfortunately, conventional vaccines for influenza require about two weeks to cause the body's immune system to build up enough antibodies to produce immunity.
As the incubation period for influenza is short, it is critical to have a means of interfering with the growth of the influenza virus within the patient in an immediate manner.
It has been known to produce a cold-adapted influenza virus material derived from an epidemic virus strain. See generally Maassab, Adaptation and Growth Characteristics of Influenza Virus at 25.degree. C., Nature, Feb. 11, 1960, 7, pages 612-614, and Maassab, Biologic and Immunologic Characteristics of Cold-Adapted Influenza Virus, the Journal of Immunology, Vol. 102, No. 3, 1969, pages 728-732. Noted in this prior art is the fact that cold variants of influenza virus showed an impaired capacity to reproduce at acid pH (5.7 to 6.3) and at elevated temperature 41.degree. C. See generally Cox et al. Virology 167, pp. 554-567 (1988) and the ability to grow at 25.degree. C. In the reported tests, these features were used as markers to differentiate the cold variant from the original wild strain. These cold variants were found to elicit good antibody responses in tests with mice, ferrets, and humans.
The advantageous use of live attenuated cold-adapted reassortant influenza A H3N2 and H1N1 virus vaccine against homologous wild-type virus seven months after vaccination has been reported. See Clements et al., Resistance of Adults to Challenge with Influenza A Wild-Type Virus After Receiving Live or Inactivated Virus Vaccine, Journal of Clinical Microbiology, Vol. 23, No. 1., pages 73-76 (1986). These attenuated cold-adapted vaccines produced results at least as great as the inactivated virus vaccines when administered to healthy persons in prophylactic doses.
The inventors of the present invention in September of 1989 reported two cold-adapted reassortants which are candidates for a live influenza A virus vaccine interfering with the replication of their parental wild-type viruses in mixed infections. The cold-adapted reassortant was also found to be able to inhibit heterologous influenza A virus, Whitaker-Dowling and Youngner, Dominants of Cold-Adapted Vaccine Strains of Influenza A Viruses and Mixed Infections with Wild-Type Virus, Genetics and Pathogenicity of Negative Strand Viruses, Elsevier Science Publishers BV, pages 402-407 (1989).